1. Field of the Invention
The present invention relates generally to photographic film units of the instant-processing type that can be handled in daylight without fogging or premature exposure because of a removable, opaque sheet which shields the photosensitive elements of the film unit from actinic or other radiation. The opaque sheet extends from within the film unit through an opening at one end of the unit, and is removed prior to making an exposure. More specifically, the invention relates to means for establishing a light seal between the opaque sheet and the interior of the film unit.
2. Background of the Prior Art
A preregistered instant processing film unit that is suitable for daylight handling is disclosed in coassigned U.S. Pat. Application Ser. No. 834,589, filed concurrently herewith and entitled INSTANT PROCESSING FILM UNIT HAVING INTERNAL DARK SLIDE. That film unit includes a photosensitive element for recording a latent image that is processable to establish a visible image, a transparent cover sheet for facilitating the distribution of a processing composition over the photosensitive element to effect such processing of the element, a reservoir for supplying the composition and an opaque sheet removably positioned between the photosensitive element and the cover sheet to protect the photosensitive element from premature exposure by radiation entering through the cover sheet. The film unit may be positioned in suitable exposure apparatus with the opaque sheet extending to a position where it is accessible for removal from between the photosensitive element and cover sheet before an exposure is made. While the exposure apparatus may take various forms, the preferred embodiment of the film unit of the present invention has particular utility in presently available professional cameras or adapters for such cameras.
In the above-identified, coassigned application, the opaque sheet is identified as an internal dark slide, and that term will also be used hereout. Under adverse handling conditions when the photosensitive element and the cover sheet may be forced apart, light may leak into the unit at the opening through which the dark slide extends from between the photosensitive element and the cover sheet. The dark slide of the coassigned application cooperates with the film unit to form a light seal which has particular advantages and generally operates satisfactorily for its intended purpose. However, under unusual operating conditions, it may suffer from certain disadvantages.